Method for making carboxy free polyamide acid salts derived therefrom

ABSTRACT

A method is provided for converting a polyimide to the corresponding polyamide acid salt, utilizing a predetermined amount of a strong base. The polyamide acid salt can be converted to the corresponding polyamide acid. The polyamide acids and polyamide acid salts provided by the subject method can be converted to the polyimide state after being applied to various substrates by standard dipcoating and electrocoating techniques. When utilized with a potentiometric titrator, the method of the invention also can be used to determine imide functionality of polyimide.

United States Patent Boldebuck 1 *July 1, 197 5 [54] METHOD FOR MAKINGCARBOXY FREE 3,528,937 9/1970 Reynolds et a1. 260/78 TF 3,529,017 9/1970Izard et a1. 260/515 P gggggf SALTS DERIVED 3,737,478 6/1973 Boldebuck260/78 UA 3,812,069 5/1974 Boldebuck 260/78 TF Edith M. Boldebuck,Schenectady, NY.

General Electric Company, Schenectady, NY.

The portion of the term of this patent subsequent to June 5, 1990, hasbeen disclaimed.

Filed: Feb. 5, 1973 Appl. N0.: 329,428

Related U.S. Application Data Inventor:

Assignee:

Notice:

Division of Ser. No. 148,154, May 28, 1971, Pat. No.

Field of Search 260/78 UA, 47 CZ, 47 CP, 260/65, 78 A, 93.5 A, 78 TFReferences Cited UNITED STATES PATENTS 3/1966 Endrey 260/78 TF OTHERPUBLICATIONS Adrova et al.: Polyimides, A New Class of Heat ResistantPolymers; 1969, pp. 65-70.

Mark et 21.: Man Made Fibers, Science and Technol- 01;); Vol. 2, 1968,p. 387.

Primary ExaminerHarold D. Anderson Attorney, Agent, or FirmWilliam A.Teoli; Joseph T. Cohen; Jerome C. Squillaro ABSTRACT A method isprovided for converting a polyimide to the corresponding polyamide acidsalt, utilizing a predetermined amount of a strong base. The polyamideacid salt can be converted to the corresponding polyamide acid. Thepolyamide acids and polyamide acid salts provided by the subject methodcan be converted to the polyimide state after being applied to varioussubstrates by standard dipcoating and electrocoating techniques. Whenutilized with a potentiometric titrator, the method of the inventionalso can be used to determine imide functionality of polyimide.

2 Claims, 3 Drawing Figures METHOD FOR MAKING CARBOXY FREE POLYAMIDEACID SALTS DERIVED THEREFROM This is a division of application Ser. No.148.154, filed May 28. 1971. now U.S. Pat. No. 3.737,478.

The present invention relates to a method of converting polyimide to thecorresponding polyamide acid salt and to certain polyamide acids andsalts made by such method.

As shown for example. by Edwards US. Pat. No. 3.l79,614. polyamide acidscan be made by reacting organic carboxylic acid dianhydrides and organicdiamines. Edwards US. Pat. No. 3,179,634, further teaches that suchpolyamide acids can be fabricated to the infusible state by theemployment of heat. It is generally known that after the fabricationstep, scrap polyimide is virtually useless. It can not be furtherfabricated, and it has substantially reduced solubility in organicsolvents. One method of salvaging scrap polyimide is by the degradationof the polymer backbone, such as shown by lzzard et al. US. Pat. No.3,529,017, showing the conversion of such polyimides derived from thereaction of organic dianhydrides and organic diamines to thecorresponding organo carboxylic acid salts. and organic diamines byeffecting the hydrolysis of the polyimide under severe conditions withexcess caustic soda. Limited success with polyimides in ftbrous form orin the form of fabrics also has been achieved. It has been found forexample, that polyimide fabric can be more readily dyed if initiallytreated with an alkaline earth hydroxide. As a result of such treatmentsites can be introduced along the polyimidebackbone. suitable forintroducing dyable aryloxypropanesulfonate units. i i y The presentinvention is based on the discovery that polyimides can be converted touseful polyamide acid salts without significant polymer degradation bycontacting the polyimide with a base, such as an alkali hydroxide or atetraalkyl ammonium hydroxide. Surprisingly. contrary to the teaching ofthe prior art, the polyimide backbone is not degraded. even though astrong base such as an alkali hydroxide is used. It has been found thateffective results are achieved if a critical amount of base is employed.More particularly, base should be employed at a concentration which issufficient to provide up to a value which does not substantially exceedone where the value is derived from the ratio of moles of available baseto moles of imide functionality of the polyimide.

There is provided by the present invention, a method for salvagingpolyimide values from polyimide by con- 1 verting such polyimide valuesto polyamide acid salt values, which comprises, adding a base to thepolyimide at a temperature up to 150C, while the polyimide issubstantially dissolved in a solvent comprising an inert aprotic polarorganic solvent, where the base is characterized by having an ionizationconstant greater than 10 in water at C, and is employed in the resultingmixture at a concentration which is at least sufficient to neutralizeany carboxy radicals which may be present. and provide a ratio of molesof base, per mole of imide functionality of the polyimide having a valueof from about 1 to 2.3.

Included by the polyimides which can be employed in the practice of theinvention, are any polyimides which are at least partially soluble in anaprotic polar organic solvent, as defined hereinafter. The polyimidescan have imide functionality in the polymer backbone,

or in the pendant position and include poly(aspartimide),

poly(amideimides)s, poly(amideacidimide)s, poly(esterimide)s, etc.;polyimides containing functional units, or polymeric blocks of organosiloxane. polycarbonate, polysulfone, polyurethane, etc., substitutedwith radicals such as, organo silyl, alkoxy, etc. Other examples,include polymers shown in Edwards ;U.S. Pat. Nos. 2,710,853, 2,867,609,and 3,179,634.

. -D/C \Q 111-1 ii i 2 HH (2) N C, NQ"

LQ Q I 2 0 0 2 and HH 0 H where Q is a divalent organo radical free ofaliphatic unsaturation and D is a member selected from -O and Some ofthe imides having units of formula (I) are shown in copendingapplication of Holub and Gaertner Ser. No. 40.802, filed May 27, I970,now abandoned, and assigned to the same assignee as the presentinvention. As disclosed by Holub and Gaertner, polyimides can be made byheating the reaction products of organic diamines of the formula,

and a benzene carboxylic acid reactant selected from a4-haloformylphthalic anhydride, or a mixture of a 4- haloformylphthalicanhydride and a phthalolylhalide. I

Polyimides having units of formula (2), or a mixtureof formula (2) and(3) units, can be made by effec'ting1 such as, -ROR,

i O II II -ROR, -RCR-, -RSR-,

etc., where R is divalent hydrocarbon.

In addition to the above described polyimides, there also can beemployed in the practice of the invention, polyimides which are made bythe method shown by Klebe and Windish, copending application Ser. No.838,322, filed July I, 1969 now abandoned, and assigned to the sameassignee as the present invention. As described by Klebe et al., variousaromatic carbocyclic organic polymers, such as polystyrene,polyaryleneoxide, polycarbonate, polyester, can be imido alkylated withan imido alkylating agent of the formula,

where R is a divalent organic radical selected from the class consistingof divalent hydrocarbon radicals and halogenated divalent hydrocarbonradicals, and R is selected from hydrogen, monovalent hydrocarbonradicals, and halogenated monovalent hydrocarbon radicals, Y is ahalogen or hydroxy radical, and m is an integer having a value of from Ito 4 inclusive.

Radicals included by R, are, for example, arylene radicals, such asphenylene, biphenylene, naphthylene, anthrylene, etc., alkyleneradicals, such as ethylene, trimethylene, tetramethylene, etc.,halogenated arylene and alkylene radicals such as chlorophenylene,chloronapathylene, chloroethylene, chlorotrimethylene, etc.;aliphatically unsaturated radicals such as,

where X is the same' or different radical selected from hydrogen, loweralkyl, halogen, such as chloro, methyl, ethyl, propyl, bromo, etc.Monovalent and hydrocarbonradicals included by R are, for example,phenyl, chlorophenyl, methyl, ethyl, propyl, butyl, pentyl, hexyl,heptyl, octyl, etc.

As taught in the above identified application of Klebe and Windish, aFriedel Crafts catalyst, such as bo'ron trifluoride is employed toimidoalkylate various aromatic carbocyclic organic polymers aspreviously defined. These polyimides have aromatic carbocyclic radicalsoccurring in either the pendant position, such as polystyrene, or thepolymer backbone, such as polyaryleneoxide, polycarbonate, polyester,etc., substituted with imidoalkyl radicals of the formula,

where R, R and m are as previously defined. Included among theimidoalkyl substituted aromatic carbocyclic polymers having imidoalkylradicals of formula (5) are organic polymers selected from backbonepolymers of the formula,

( 3 gaw (2)-j and and pendant polymers of the formula,

I )5 l c 4-(z') i v a lll I J where R" is a polyvalent organo radical,such as an aromatic carbocyclic radical having from 6 to 18 carbonatoms, R' is a monovalent aromatic carbocyclic radical having from 6 tol8 carbon atoms, X is as previously defined. Z and Z are divalent organoconnectives defined below. a is a whole number equal to (J or 1, and nis an integer having a value of from 1 to 1.000 inclusive.

Radicals included by R" of Formula 6 are phenylene, tolylene, xylylene,naphthylene. anthrylene, etc.; halogenated derivatives of such aromaticcarbocyclic radicals. alkylated derivatives of such aromatic carbocyclicradicals: a mixture of such aromatic carbocyclic radicals. orderivatives of such aromatic carbocyclic radicals, and other polyvalenthydrocarbon radicals or halogenated polyvalent hydrocarbon radicals,which mixture contains at least about 1 percent and preferably about 10mole percent to 99 mole percent of such aromatic carbocyclic radicals orderivatives thereofand up to 99 mole percent. and preferably up to about90 mole percent of divalent radicals such as alkylene radicals. forexample. methylene, ethylene. trimethylene, etc., halogenatedderivatives thereof. etc.

Radicals included by R' of formula (7) are, for example. phenyl. tolyl.xylyl, naphthyl. anthryl. etc.; halogenated derivatives of suchmonovalent aromatic carbocyclic radicals; alkylated derivatives of suchmonovalent carbocyclic radicals; a mixture of such aromatic carbocyclicradicals, and other monovalent hydrocarbon radicals or halogenatedhydrocarbon radicals, which mixture contains at least about 1 molepercent and preferably 10 mole percent to 99 mole percent of sucharomatic carbocyclic radicals, or derivatives thereof. and up to about99 mole percent and preferably up to 90 mole percent of monovalentradicals such as alkyl radicals. for example, methyl, ethyl, propyl.butyl, etc.; halogenated derivatives thereof. etc. In Formula (6), Z isa polyvalent organo connective such as,

I! ll -O-, -CO-, -OCO- and mixtures thereof; Z in Formula 7 is adivalent organo connective, such as etc., Q is a polyvalent aliphaticradical.

The bases which can be employed in the practice of the invention are anyorganic or inorganic bases having an ionization constant greater than 10and preferably greater than 10 in water at 25C. There can be employedbases included by the formula,

MOI-l,

where M is a member selected from alkali metal ions and tetraorganoammonium ions. In instances where M is alkali metal, M also can bechemically combined with OG radicals where G is selected from alkylradicals and aryl radicals. Included by the bases which can be employedare for example, alkali metal hydroxides, such as sodium, potassium,lithium, etc.; tetraalkyl ammonium hydroxides, such as tetramethyl,tetrabutyl, etc., alkoxides, such as sodium methoxide, potassiumethoxide, etc., phenoxides, such as sodium phenoxides, potassiumphenoxides, etc. In addition, organic bases such as guanadine, etc., andalkali metal salts of weak acids having acid dissociation constants of10 or less, which produces alkali metal hydroxides insitu in aqueoussolutions also can be employed.

The polar organic solvents which can be employed in the practice of theinvention are preferably polar aprotic solvents chemically inert to thereactants during the practice of the invention. Some of the solventswhich can be employed are for example, N,N-dimethylformamide,N,N-dimethylacetamide, N,N-diethylformamide, N,N-diethylacetamide,N,N-dimethylmethoxy acetamide, N-methyl caprolactam, dimethylsulfoxide,N-methyl-Z-pyrrolidone, tetramethyl urea, pyridine, dimethylsulfone,tetramethylene sulfone, N- methylformamide, N-acetyl-2-pyrrolidone. Inaddition, other diluent solvents substantially inert during the practiceof the method can also be utilized, such as aliphatic hydrocarbons,alcohols, ethers, etc.

An additional feature of the present invention is directed to thepolyamide acid salts and polyamide acids which can be derived inaccordance with the practice of the invention from polyimides havingradicals of Formulas 2, 3 and 5. Some of these polyamide acid salts arearomatic carbocyclic polymers consisting essentially of units ofFormulas (6) or (7) above, substituted with amide acid salt radicals ofthe formulas,

0 H H 8 R--CN (m COM R where R, R, M and m are as previously defined.Additional polyamide acid salts can be derived from polyimides havingchemically combined units of Formulas (2) or (3) in accordance with themethod of the invention, which can have units included by the formulaswhere Q is as previously defined.

Included by the polyamide acid salts having radicals of Formula (8)which are provided by the invention are, for example, aromaticcarbocyclic backbone polymers, such as polyaryleneoxides havingchemically combined units of the formula,

c c=ccoM,

aromatic carbocyclic pendant polymers, such as polystyrene havingchemically combined units of the formula,

------CH2N-C: 3

MOC

0 etc which can be derived in accordance with the present invention frompolyamide acid salts having units of Formulas (9) and 10) or mixturesthereof, where Q is as previously defined.

In the practice of the method of the present invention, a predeterminedamount of strong base is added to polyimide in the presence of polarorganic solvent. The amount of base added should be sufficient to effectthe conversion of at least one, and up to the total amount of the imideradicals in the polyimide to the corresponding polyamide acid salt.

The employment of excessive amounts of base must be avoided to minimizepolymer degradation. It has been found desirable to know the imidefunctionality of the polyimide before the base is added to thepolyimide-organic solvent mixture. In instances where imide is employedhaving chemically combined imide and non-imide nitrogen, ordinarytechniques used for determining total nitrogen, such as the Kjeldahlmethod are not satisfactory for distinguishing imide nitrogen fromnon-imide nitrogen. A convenient way of determining imide functionalityin polyimide which can distinguish imide and non-imide nitrogen is byemploying a potentiometric titrator. A titration curve can be plotted asshown by FIGS. 13, depending upon the type of polyimide used in thetitration, and an end point in meq of base consumed will indicate thenature of the polyimide.

The titration curve of FIG. 1, for example, can be obtained whentitrating with base utilized in the practice of the invention todetermine imide functionality in a polyimide having chemically combinednon-imide nitrogen such as polyamideimide.

In instances where the polyimide has free carboxy radicals on thepolymer chain, such as amide acid groups, base concentrations sufficientfor the neutralization of these carboxy radicals, in addition to imidering opening should be employed. As shown in FIG. 2, neutralizatiton ofthe carboxy radicals, will proceed prior to the stage at which ringopening of the imide groups will occur.

In instances where the polyimide contains only chemically combined imidenitrogen, for example, aromatic carbocyclic polymers of Formulas (6) or(7) substituted with radicals of Formula (5), a standard nitrogenanalysis for weight percent nitrogen, such as the Kjeldahl method can beemployed, or optionally potentiometric titration can be used employingbase utilized in the practice of the present invention. As shown by thecurve in FIG. 3, if the total base used is added in increments, twotitration curves, Curve A and Curve B can result. Curve A shows theinitial reading, after each increment of base is added, while Curve Bshows the results obtained after a time dependant drift-back associatedwith slow consumption of base to form salt has stabilized.

More particularly, FIG. 1 further illustrates how potentiometrictitration can be used to determine imide functionality, in a polyimidefree of carboxy radicals and containing non-imide nitrogen, such asfound in a such as polymers of Formulas (6) and (7) substituted withmaleimidomethyl radicals can produce potentiometric curves resemblingFIG. 1.

There is also provided by the present invention, electrocoatingcompositions of polyamide acid salt compositions having chemicallycombined units of Formulas (8), (9). and 10) or mixtures thereof.organic solvent and water which can be in the form of a dispersion orsolution. These electrocoating compositions can have polyamideimide. Theabscissa shows meq of base, per 5 from about-0.5 to about percent solidsbased on the gram of polyimide, and the ordinate is expressed in milweight of mixture. The liquid phase can comprise from livolts. Thedotted line indicates how a typical curve about 10 to 90 percent waterand from 90 to 10 percent would appear which had a trace acid as animpurity. by weight of organic solvent. as previously defined. Normally.the solid line shows the relationship between There can be from about 5mole to 100 mole of the results obtained by adding base to the mixtureand 10 units of Formulas (8), (9), or 10), respectively, based shows theend point. Total imide functionality can be on the total moles of suchunits, and units of Formulas calculated directly from the curve at theend point, 3 or 3 or 5 respectivgly i h polyimide which corresponds tocomplete neutralization Of the In order that those skilled in the artwill be better able amide Add generated to practice the invention, thefollowing examples are Knowing the weight of the sample in grams, thetotal 5 iv by way of illustration and not by way of1i i moles of imidecan be readily calculated in the sample i All parts are b i h utilizedby the following relationship: EX M E 1 A polyimide was prepared fromequal molar amounts cc of base X normality of huge Of dN,N'-4.4-diphenylmethane bismaleimide and \vcightof polymer samplebis(4-aminophenyl)methane, in accordance with the teaching of US. Pat.No. 3,562,223, Bargain et al. The weight of polymer associated with oneequivalent Ba ed on meth d f preparation, h resulting l of functionalgroup also can be calculated by the fori id h d 3 6()5 illi i l m or meqf i id per mulfli gram of sample.

The above polyimide was then titrated, to determine the meq of imide,per gram of sample. A 0.15 percent 1000 mcq of functional group/gram ofpolymer solution of the polymer in di methyl formamide was t1- tratedpotentlometrlcally with methanolic tetrabutyl FIG. 2 is moreparticularly a typical curve obtained ammonium hydroxide' There wasemployed Beck from a polyimide having available carboxy radicals, manZeromanc pH w glass electrode and a Cale such as normally present in apolyamide acid which is melelectrodmodlfied wlth Saturated mfethanoliceither partially or substantially imidized. Again the dottasslum Chlondel' After h lncremem of ted line on the curve indicates the typicalshowing of a the meter mdlcated large mllhvolt change polyamide acidhavingdtrace ofastrongacidimpurity, which then slowly drifted back to alesser millivolt which is shown as Acid l. Acid II is shown at the pointreadmg and Stabilized The end Point Obtained indi of completeneutralization of the amide acid. The final Camd meq of imide per gramof Sample- This inflection in the Curve shows the point at which thesult compared favorably with the theoretical of 3.605. completeconversion of the imide functionality in the A Solution was P p from theabove P y polyimide to the amide acid salt has been effected. utilizing1252 Parts Of P y P 2319 Parts of Total moles of imide. as well as thetotal moles of carmethyl py To this solution there was added boxy in thepolyamide acid can be readily be calculated 012 Parts of tstrabutylammonium hydroxide in the by using the above relationships. form of amethanolic solution. After 5 minutes 7.226 FIG 3 is a Curve Obtained bytitrating Certain l i parts of water was slowly added to the mixturewith stirmides having chemically combined radicals of Formu g A smallamount of Coagulation was Observed and las l-3 or 5, includingphthalimidomethyl substituted n ion 7.2 p r of N-m hyl pyrr li ne waspolystyrene or polyaryleneoxide. Curves A and B in added to redissolvethe polymer. An additional 0.667 FIG. 3, show a time dependentrelationship of the efparts of water was added to produce a slightlyhazy stafects of added increments of strong base to the poly- SO blesolution. Based on method of preparation, the miximide. Drifting backfrom Curve A to Curve B occurs ture was a solution of a polyamide acidsalt having upon the conversion of the imide functional group tochemically combined units of the formula.

I? n H H N CH NC-C-N-CH NH I COOM the amide acid salt. The cycle isrepeated after each ,0 where M is 11 IBtYahUtYIammOHiUm i011-stablilization had been effected until the end point is Employing a 1inch wide Copper foil anode and a I achieved establishing that there hasbeen an amount of inch wide Platinum foil Cathode, at a 1/2 inch p i ntitrant employed sufficient to provide up to about one there was passeda 40 ma constant current through the mole of base. per mole of imide. Italso has been found above electrocoating composition for 1 minute usingthat certain polyimide having units of Formula (5), the aforementionedelectrodes at a 1 inch immersion.

There was obtained O.l838 part of wet film on the anode, which washeated for 1 minute at C and 5 minutes at 250C. A solvent-free polyimidecoating, weighing 0.0205 part was obtained. It was light brown in color,glossy and adherent. Where the copper foil was bent and creased, thefilm did not crack. The weight of a comparable dip coating film afterthe same cure, was 0.0004 part. The valuable insulating characteristicsof the film are established by utilizing it as an electrode in a dilutesolution of hydrochloric acid. It is found that the surface of the filmis free of bubbles showing that there is no curent flowing.

A solution also was prepared of the polymer made in accordance with theabove described Bargain et a1, except that no base was added. Noelectrodeposit was obtained when a 40 ma current was passed through themixture following the same procedure.

EXAMPLE 2 A polyaryleneoxide having chemically combined 2,6-diphenylphenoxy units substituted with phthalimidomethyl radicals wasdissolved in dimethyl formamide, utilizing one part of polymer, per36.75 parts of solvent. Based on the titration method of Example thepolyimide had about 52 mole percent of such phthalimidomethylsubstituted phenoxy units, based on the total moles of phenoxy units inthe polyaryleneoxide. The polyaryleneoxide was made by the abovedescribed method of Klebe as shown in copending application Ser. No.838,322, utilizing phthalimidomethyl chloride as an imido alkylatingagent. To the aforementioned solution there was added 0.8 millimoles oftetrabutyl ammonium hydroxide dissolved in methanol and the mixture wasstirred for 15 minutes. There was then added 12.52 parts of water,resulting in a faint haze. Based on method of preparation, there wasobtained a solution of a polyaryleneoxide having chemically combinedpolyamide acid salt units of the formula,

COOM

Wet Deposit (g) Cured Film (g) Copper .5172 .0257 Aluminum .5132 .0221

The above films were found to possess valuable insulatingcharacteristics when subjected to the conductivity test described inExample 1.

The above procedure was repeated with the same polyaryleneoxidesolution, except no base was added. It was found that the solution couldnot be electrocoated.

EXAMPLE 3 A phthalimidomethyl substituted poly( 2,6-dimethylphenyleneoxide) was prepared in accordance with the abovedefined Klebe method. Based on a Kjeldahl weight determination, thenitrogen analysis of the polymer was found to be 2.37 percent.

The polymer was titrated in accordance with the above describedprocedure of Example 1. using a 0.33 percent solids solution andtetrabutyl ammonium hydroxide. Based on the titration, the polymer had1.67 meq of imide, per gram of polymer. This indicated there was 593grams of polymer, per imide functionality or a nitrogen weight percontent of 2.36 percent. Based on method of preparation, and thenitrogen content of the polymer the mixture was a solution of apoly(phenyleneoxide) having mole percent of chemically combined amideacid units of the formula,

v CH 5 NH I i) MO-C where M is tetrabutyl ammonium ion.

An electrocoating solution was made from the above phthalimidomethylsubstituted polyphenyleneoxide, consisting of 2 percent by weight ofpolymer solids, 76 percent of dimethylformamide, and about 22 percent byweight of water. There was added to the solution a sufficient amount oftetrabutyl ammonium hydroxide to convert 27 mole percent of thephthalimidomethyl groups to amide acid salt groups. Based on thecalculation that the polymer had 27 mole percent of chemically combinedamide acid salt groups, its equivalent weight was 2200 grams, per amideacid salt group.

There was passed 10 ma constant current for 1 min ute through the aboveelectrocoating mixture, which was equivalent to 0.6 coulombs. The amountof polymer solids deposited on the copper anode weighed 0.0139 partafter removal of solvent by heating the film for 5 minutes at 250C. Thisindicated that its equivalent weight was 2300 grams, or there was 2300grams of polymer deposit per Faraday.

EXAMPLE 4 A polyamideimide containing free carboxy radicals was made byeffecting reaction of 0.45 moles methylene dianiline and 0.50 molestrimellitic anhydride in a l to l N-methylpyrrolidone xylene blend. Themixture was heated to a temperature of 225C with stirring untilapproximately the theoretical amount of water was collected. AdditionalN-methyl pyrrolidone was added to produce a mixture having 51 percentsolids.

There was added 47.2 parts of p,p-diphenylmethane diisocyanate dissolvedin 100 parts of N- methylpyrrolidone to about 325 parts of the abovemixture, which was then heated up to 180C and diluted with 181 partsN-methylpyrrolidone. There was obtained a polyamideimide, having 0.52meq carboxy groups, and 2.38 meq of imide groups per gram of polymericsolids, as determined by potentiometric titration.

The above polyamideimide was dissolved in N methyl pyrrolidone toproduce a solution having 1 /2 parts of polymer and 39 parts of solvent.There was initially added sufficient aqueous sodium hydroxide toneutralize the free carboxy radicals in the mixture. There was thenadded 9 parts of water to the mixture, which caused agglomeration of thepolymer. Additional N-methyl pyrrolidone was then added to produce aclear solution containing 2.4 percent polymer. 83.4 percent N-methylpyrrolidone and 14.2 percent water. An attempt was made to electrocoatthis solution and it was found that electro-deposition ofthe polymer didnot occur utilizing the apparatus and procedure of Example 1.

The same polyamideimide solution was prepared by the above procedure.There was then added 1.62 meq of sodium hydroxide to the mixture. Thisconcentation was sufficient to completely neutralize all free carboxyradicals. and convert about 30 mole percent of the available imidegroups to amide acid salt groups. The resulting mixture containing 1parts of polymer dissolved in 39 parts of N-methyl pyrrolidone. Inaddition, to the added amount of base as previously described, water wasthen added to the mixture to produce a mixture having by weight 2percent polymer, 64.1 percent N-methyl pyrrolidone and 33.4 percentwater. The solution was then employed in the electrocoating apparatus ofExample 1. and the electrocoating of the mixture was repeated. When a 40ma constant current was employed for 1 minute. utilizing an alluminumanode, 0.018 part of polymer was obtained on the anode after removal ofsolvent. The resulting polyimide film was found to exhibit valuableinsulating properties.

EXAMPLE A polyamideimide substantially free of free carboxy radicals wasmade by reacting diphenylmethane diisocyanate and trimellitic anhydridein a mixture of N- methyl pyrrolidone and dimethyl acetamide inaccordance with the method of S. Terney, J. Keating and J. Zielinski.Journal of Polymer Science. P. 686, Vol. 8. (1970). By titratingpotentiometrically with tetrabutyl ammonium hydroxide. the polymersolution was found to contain 0.767 meq of imide per gram of solution,and less than 0.04 meq of free carboxy radicals. The polymer solidscontent was 0.268 g per gram of solutron.

After the exact imide functionality of the dissolved polyamideimide wasdetermined as described above, it was possible to prepare a polyamideacid salt of the polyamideimide. Accordingly. there was added to 18.63parts of the polymer solution an additional 48 parts of N-methylpyrrolidone and sufficient meq of aqueous sodium hydroxide to completelyconvert imide functionality to amide acid salt functionality. Thespecific resistivity of the solution was found to be 1140 ohmcentimeter.

An organic strong acid cation exchange resin in the form of sulfonatedpolystyrene copolymer in the hydrogen form, having an exchange capacityof 2.29 meq per gram, was washed 5 times with distilled water. thenwashed 3 times with dry N-methyl pyrrolidone. There was then added 9.4parts of the washed ion exchange resin to the above polyamide acid saltsolution. The resulting mixture was stirred for minutes and filtered.There was obtained a clear polyamide acid solution having a specificresistance of 8900 ohm centimeter.

An electrocoating composition was made from the above describedpolyamide acid, by the addition of ammonium hydroxide in an amountsufficient to neutralize percent of the amide acid groups in theresulting polymer solution. This polyamide acid ammonium saltcomposition was compared to an electrocoating composition of the samepolyamideimide reacted with the same meq of sodium hydroxide in place ofammonium hydroxide. When both compositions were employed in theelectrocoating apparatus of Example 1, it was found that essentiallyidentical results in terms of electrodeposited films on copper wereobtained. These results are shown in the following table, Na is thepolyamide acid sodium salt, and NH; is the polyamide acid ammonium salt.

weight 7! of grams of polymer in deposit polymer deposited Na NH,

EXAMPLE 6 A phthalimidomethyl substituted polystyrene was made inaccordance with the above described Klebe method, utilizingphthalimidomethyl chloride, boron trifluoride, and polystyrene. Theresulting polymer was titrated as a 0.1 percent solution in dimethylformamide with tetrabutyl ammonium hydroxide. The polymer was found tohave about 1.99 meq imide groups, per gram of polymer.

A polyamide acid salt composition was prepared from the above polyimide.Tetrabutyl ammonium hydroxide was used in amounts sufficient to convertall of the imide groups of the polyimide to the corresponding polyamideacid salt groups. Based on method of preparation, there was obtained asolution of a polyamide acid salt having about 30 mole percent ofchemically combined units of the formula,

O OM HNC where M is a tetrabutyl ammonium ion.

The above solution was then acidified with glacial acetic acid and thetotal mixture was then added to a large excess of water. The pH of theresulting aqueous phase was approximately 7. A fiocculent precipitatewas obtained which was filtered, washed several times with water,filtered again and then dried in air for several hours. Based on methodof preparation, the product was a polyamide acid substitutedpolystyrene, having about 30 percent of the styrene rings substitutedwith polyamide acid units in the form of polyamide acid phthalamidomethyl units of the formula,

The above polyamide acid was dissolved in dimethyl formamide, andanalyzed for polyamide acid content and imide content. It was found thatthe polymer was free of imide groups and contained about 1.14 meq ofamide acid groups per gram of polymer. The polyamide acid wasneutralized with ammonium hydroxide and the resulting solution waselectrocoated utilizing the apparatus of Example 1. There was obtainedan electrodeposit of material which produced a polyimide exhibitingvaluable insulating properties when the copper anode having theelectrodeposited product was heated as in Example 1.

EXAMPLE 7 A polyarylene oxide consisting essentially of chemicallycombined 2,6-diphenylphenoxy units and substitued with phthalimidomethylradicals was prepared by the above described method of Klebe. Thephthalimidomethyl substituted polyarylene oxide was titrated indimethylformamide in accordance with the present invention to determineits imide content using tetrabutyl ammonium hydroxide. The polymer wasfound to have 1.4 meq of imide groups, per gram of polymer.

Two parts of the above polyimide was dissolved in 38 parts of dimethylformamide. There was added all at once to the resulting solution,sufficient tetrabutyl ammonium hydroxide in the form ofa 1 normalmethanolic solution to completely convert the polyimide to the polyamideacid salt state. The pH of the resulting mixture was approximately 8.Based on method of preparation there was obtained a solution of apoly(aryleneoxide) having chemically combined units of the formula,

where M is a tetrabutyl ammonium ion.

A portion of l N aqueous hydrochloric acid was added with stirring toproduce a mixture having a pH of about 6.5. The mixture was then pouredinto a large volume of water. A finely divided gelatinous precipitateresulted which was filtered under suction and washed several times withwater, to produce a slightly damp product. Based on method ofpreparation the product was a polyaryleneoxide having chemicallycombined polyamide acid units of the formula,

The above polyamide acid was neutralized with ammonium hydroxide. Theresulting polyamide acid ammonium salt solution was then electrocoatedonto a copper anode. When the copper anode was heated, as described inExample 1, a polyimide film was obtained exhibiting valuable insulatingproperties.

EXAMPLE 8 A maleimidomethyl substituted polystyrene was made by theabove described method of Klebe utilizing maleimidomethyl chloride as animidoalkylating agent. The polymer was found to contain 0.189 meq ofimide groups per gram of polymer, employing the method of Example 1.

One part of the above maleimidomethyl substituted polystyrene wasdissolved in 50 parts of dimethyl formamide. There was then addedmethanolic tetrabutyl ammonium hydroxide in amounts with stirring, toconvert the polyimide to the corresponding polyamide acid salt. Acharacteristic deep red solution resulted. Based on method ofpreparation, there was obtained a polystyrene having chemically combinedunits of the formula,

where M is a tetrabutyl ammonium ion.

There was added to the mixture, 35 parts of water. The mixture waselectrocoated and a polyimide film was made on copper and aluminumanodes, exhibiting valuable insulating characteristics.

EXAMPLE 9 The polyamideimide prepared in Example 4, dissolved inN-methyl pyrrolidone. having a 0.52 meq carboxy/gram of polymer. and2.38 meq imide per gram of polymer was used to prepare a series ofelectrocoating compositions employing alkali metal alkoxides, alkalimetal phenoxides and alkali metal salts of weak 18 solids and solvent inthese electrocoating compositions are the same as the electrocoatingcompositions previously described.

In order that those skilled in the art will be better able acids. Eachof the electrocoating compositions were to practice this aspect of thepresent invention, the folprepared with 4 parts ofa 27.6 percent polymersolulowing example is given by way of illustration and not tion whichwas adjusted to 3.7 percent of poymer solids by way of limitation. Allparts are by weight. in N-methyl pyrrolidone prior to the addition ofbase and dilution with water. The following table shows the EXAMPLE baseemployed in each composition and the ingredients l0 Polyimide A" wasprepared in accordance with the of the compositions expressed in percentby weight of method of Example 9, having 2.53 meq of imide per polymer,solvent. and moles of base/gram of polymer. gram of polymer. andsubstantially free of carboxy radi- ELECTROCOATING COMPOSITIONS Weight7! BASE 72 Polymer NMP Water Alcohol Millimoles base per g polymer ASodium ethoxide 2.5 66 18.5 13.0 1.98 B Sodium phenoxide 2.5 58 32.4 7.11.98 C Sodium carbonate 2.5 64.8 32.7 2.17 D Sodium carbonate 2.5 65.132.4 1.10 E Sodium bicarbonate 2.5 65.1 32.4 1.14 F Trisodium phosphate64.9 32.6 1.52 G Sodium hydroxide 2.5 65.0 32.5 1.08

ELECTRODEPOSIT 0N ALUMINUM cals. In addition to polyimide A. there alsowas pre- BASE WET CURED FILM O pared polyimide B effecting reactionbetween equal WEIGHT WElGHT molar amounts of chloroformal phthalicanhydride and methylene dianiline. Polyimide B had 1.29 meq of free ASQdiUm ethoxidc 243 m2 acid groups per gram of polymer and 1.49 meq ofimide B Sodium phenoxidc .154 .011 groups per gram of polymer. PolyimideA also had an giggly; 23:33:31; 12;; -81; 25 intrinsic viscosity of 0.31g/dl and polyimide B had an E Sodium bicarbonate I intrinsic viscosityof 0.34 g/dl when measured under F Trisodium phosphate .249 .037 th Samediti G Sodium hydroxide .071 .020

electrocoating compositions were prepared from the above polyimidesutilizing the same weight proportions There also is provided by thepresent invention. elecof polyimide, aqueous sodium hydroxide. water andN- trocoating compositions comprising polyimide substanmethylpyrrolidone. The respective electrocoating tially free of carboxyradicals, which have about 0.1 to compositions contained by weight about4.3% polymer about 1 meq of polyamide acid salt radical per gram ofsolids, 63.4% of N-methyl pyrrolidone and 32.2% of polymer. Theseelectrocoating compositions exhibit su- Water. In solutions A and B,prepared from polyimide perior shelf life stability and provide a highweight of A and B respectively, there Were approximately 0.52 polymerdeposit per coulomb of electrical charge, remeq of sodium carboxylateradicals per gram of polyf rred to sometimes as coulomb yield." The termmer. Solution A, however, had no free carboxy radicals shelf lifestability" as used hereinafter, will signify the and 2.01 meq 0f imideper gram of polymer. Solution ability of the electrocoating compositionto resist B had 0.77 meq of carboxy radicals and 1.49 meq of change overat least a 5 day aging period. Change can imide p r g 0f p y r. bemeasured with respect to percent change in wei ht The aboveelectrocoating solutions were employed to percent solids of theelectrodeposit after the shelf peelectrodeposit polyimide onto aluminumanodes, emriod. A change of 50 percent or greater in weight per- P y aCurrent density of 20 ma P Square inch cent of polymer solids indicatesthat the electrocoating 1 minute- Electrodeposition was effected aftereach of compositions are unsuitable for providing polyimide (hi1Compositions had been freshly P p and after coatings on the conductingsubstrate. Experience has a 5 y Shelf aging p It was found that both@166- shown that polyimides having polyamide acid l ditrocoatingsolutions wre substantially equivalent when c315 within the abovedefined range can not be emfreshly prepared with respect t0 providingabout 0.17 ployed to make electrocoating compositions having part of wetdeposit having 24% solids on the aluminum satisfactory shelf stabilityif the polyimide has a subanode and 0.04 part of cured polyimide film onthe alustantial amount of free carboxy radicals. minum anode. However,after a 5 day aging period, so-

ln making the polyimide electrocoating compositions lution B provided anelectrodeposit containing only 8% of the present invention, exhibitingboth high coulomb solids, indicating a significant change had takenplace yield and satisfactory shelf stability over an extended withrespect to its electrocoating characteristics. Elecperiod of time, theremust be employed polyimide subtrocoating solution A, however, remainedunchanged stantially free of carboxy radicals or polyimide havingcarboxy radicals present at up to about 0.8 meq of carboxy radicals/gramof polyimide. The weight percent of after a 12 day aging period and foran indefinite time thereafter. There was obtained from solution Aessentially the same weight of wet and dry electrodeposit after anextended aging as obtained when freshly prepared. This indicated thatthe electrocoating compositions of polymer B was unsuitable forelectrocoating purposes because of the rapid change in weight percent ofsolids in electrodeposit. Experience has shown for example, that whenthe solids content of the electrodeposit drops below about percent, thatthe conversion of the electrodeposit to the polyimide state isuneconomic. due to the solvent removal requirements. Those skilled inthe art would know that the electrocoating solution A would besatisfactory for electrocoating purposes.

Although the above examples are limited to only a few of the polyamideacid salts, polyamide acids and electrocoating compositions provided bythe present invention, it should be understood the present invention isdirected to a much broader class of such materials as shown by Formulas8-1 1 and method for making such materials. In addition. it should beunderstood that the present invention as directed to salts of the novelpolyamide acids of the invention, as shown by formula l l), which can bemade with weak bases such as ammonia, organic amines such asethanol-amine. morpholine. tertiary organic amines, etc.

What we claim as new and desire to secure by Letters Patent of theUnited States:

' l. A method for producing resinous polyamideimide substantially freeof carboxy radicals and having from 1 to 2.3 meq. of polyamide acid saltradicals per gm. of polyamideimide. which comprises, adding a base to aresinous. carboxy-free polyamideimide at a temperature up to l50C..while the polyamideimide is substantially dissolved in solventcomprising an inert aprotic organic solvent, where the base ischaracterized by having an ionization constant greater than 10 in waterat 25C.. and is employed in the resulting mixture at a concentrationwhich is at least sufficient to neutralize any carboxy radicals whichmay be present and provide a ratio of moles of base, per mole of imidefunctionality of the polyamideimide having a value of from about 0.01 toabout 1.2, whereby resinous imide values are converted to amide acidsalt values.

2. A method in accordance with claim 1, where the polyamide-imide is theresinous carboxy-free reaction product of p,p'-diphenylmethanediisocyanate and the product of reaction of methylene dianiline andtrimel-

1. A METHOD FOR PRODUCING RESINOUS POLYAMIDEIMIDE SUBSTANTIALLY FREE OFCARBOXY RADICALS AND HAVING FROM 1 TO 2.3 MEQ. OF POLYAMIDE ACID SALTRADICALS PER GM. OF POLYAMIDEIMOIDE, WHICH COMPRISES, ADDING A BASE TO ARESINOUS CARBOXYFREE POLYAMIDEIMIDE AT A TEMPERATURE UP TO 150*C., WHILETHE POLYAMIDEIMIDE IS SUBSTANTIALLY DISSOLVED IN SOLVENT COMPRISING ANINERT APROTIC ORGANIC SOLVENT, WHERE THE BASE IS CHARACT WATER AT 25*C,AND IS EMPLOYED IN THE RESULTING MIXTURE AT A CONCENTRATION WHICH IS ATLEAST SUFFICIENT TO NEUTRALIZE ANY CARBOXY RADICALS WHICH MAY BE PRESENTAND PROVIDE A RATIO OF MOLES OF BASE, PER MOLE OF IMIDE FUNCTIONALITY OFTHE POLYAMIDEIMIDE HAVING A VALUE OF FROM ABOUT 0.01 TO ABOUT 1.2WHEREBY RESINOUS IMIDE VALUES ARE CONVERTED TO AMIDE ACID SALT VALUES.2. A method in accordance with claim 1, where the polyamide-imide is theresinous carboxy-free reaction product of p,p''-diphenylmethanediisocyanate and the product of reaction of methylene dianiline andtrimellitic anhydride.